Device for the display of colour television images

ABSTRACT

A display device for colour television images, comprising a cathode-ray tube having three electron beams arranged in one plane and a deflection system comprising a ring core. On the rear of the ring core two recesses are provided at the extremities of a diameter of the ring core which is situated in the said plane.

United States Patent Talsma June 24, 1975 3,310,763 3/1967 Thompson 335/213 SIO I G 3,321,724 5/1967 Obert 4 l r 335/213 3,430,169 2/1969 GabOr 335/2l3 Primary Examiner-G. Harris Attorney, Agent, or FirmFrank R. Trifari; Henry I. Steckler [57] ABSTRACT A display device for colour television images, comprising a cathode-ray tube having three electron beams arranged in one plane and a deflection system comprising a ring core. On the rear of the ring core two recesses are provided at the extremities of a diameter of the ring core which is situated in the said plane.

8 Claims, 6 Drawing Figures [75] Inventor: Tjitte Talsma, Emmasingel,

Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, NY.

[22] Filed: Feb. 25, I974 [21] Appl. No.: 445,909

[30] Foreign Application Priority Data Mar. 19, I973 Netherlands 7303773 [52] US. Cl. 335/210; 335/213 [51] Int. Cl. H0" 7/00 [58] Field of Search 335/210, 213

[56] References Cited UNITED STATES PATENTS 3.246,l92 4/1966 Torsch 335/213 X PATENTED JUN 2 4 I975 Fig.2c

Fig. 20

Fig.2b-

Fig.4

Fig.3

DEVICE FOR THE DISPLAY OF COLOUR TELEVISION IMAGES The invention relates to a device for the display of colour television images, comprising a cathode-ray tube of the shadow mask type having a rearmost cylindrical part in which one or more electron guns are arranged for generating a number of electron beams which are situated substantially in one plane. and a foremost flared part. the said device furthermore comprising a deflection system which is coaxially arranged about the tube near the transition between the two parts of the tube and which essentially consists of an annular ferromagnetic core. a first deflection coil system for deflecting the electron beams in a first deflection perpendicular to the tube axis and in the said plane, and a second deflection coil system for deflecting the electron beams in a second deflectin direction perpendicular to the tube axis and to the said plane, the said deflection system being adapted such that the second deflection coil system generates a magnetic field which has a cushion-like shape near the rear of the deflection system and a barrel-like shape near the front. A device of this kind is known from Netherlands Pat. No. H0569.

If. for example, three electron guns are arranged one adjacent to the other in the cathoderay tube. the three electron beams generated by the electron guns are situated in a horizontal plane. The second deflection coil system then serves for the deflection of these beams in the vertical direction (referred to as the y-direction hereinafter), for which purpose it generates a magnetic field which extends mainly in the x-direction which is perpendicular to the deflection direction. It was found in practice that the field strength is location-dependent and that it contains a y-component H in addition to an x-component H,, For a given value of z (the third coordinate. the value of which increases from the electron guns in the forward direction). the field strength of the vertical deflection field can be represented as:

H,, 2H,,.\ (I) Terms of a power higher than the second are ignored in this respect, and the values H" and H are only dependent of e. In the plane X=O. H,,= and HERA-H y; this formula is also stated in Netherlands Pat. No. l l0.569. It appears from this patent specification that, in order to achieve proper convergence, H must be negative on the foremost end of the deflection system and positive on the rearmost end. As will be obvious from l as negative value of H implies that the magnetic field has a barrel-like shape, whilst a positive value implies that the field has a cushion-like shape. The said Patent Specification also describes how the requirements imposed as regards the deflection field can be satisfied by a suitable choice of the shape and the distribution of turns of the deflection coils. However. it was found in practice that the winding of such coils in large numbers with the desired accuracy is difficult. Moreover, this shape of the coil gives rise to raster distortion which must be corrected by adaptation of the deflection current.

The invention has for its object to provide a device of the kind set forth in which the desired shape of the deflection field for the second deflection direction is achieved without the said drawbacks occurring. To this end, the device according to the invention is characterized in that on the rear of the ring core recesses are provided in two diametrically situated locations. the connecting line between the recesses being substantially situated in the plane of the electron beams.

It was found that the best result can be obtained when the boundary of the recesses is a smooth line.

The invention will be described in detail hereinafter with reference to the drawing. Therein.

FIG. I is a diagrammatic longitudinal sectional view of an embodiment of a device according to the invention.

FIGS. 2a-c show the vertical deflection field at three locations in the device shown in FIG. 1,

FIG. 3 is a side elevation ofa ring core used in the device of FIG. I, and

FIG. 4 is a rear view of the ring core shown in FIG. 3.

The device for the display of colour television images which is shown in FIG. I comprises a cathode-ray tube of the known shadow mask type. comprising a rearmost cylindrical portion 1 and a foremost flared portion 3 which has a colour selection electrode (shadow mask) and a display screen (not shown) arranged on its widest end. In the rearmost portion of the tube three electron guns 5 for generating three electron beams in a horizontal plane are adjacently arranged. For the deflection of these electron beams a deflection system 7 is coaxially arranged about the tube at the area of the transition between the rearmost tube part 1 and the foremost tube part 3. The deflection system 7 comprises an annular ferromagnetic core 9, the shape of which is adapted to the flared shape of the tube. a first deflection coil system 11 for deflecting the electron beams in the horizontal direction (perpendicular to the plane of the drawing). and a second deflection coil system 13 for deflecting the electron beams in the vertical direction. Each of the deflection coil systems 1], l3 consists of a pair of diametrically arranged saddle-like deflection coils, the shape of which is also adapted to the flared shape of the tube. The magnetic fields generated by these deflection coil systems satisfy the requirements imposed in the said Netherlands Pat. No. l l0,569. For the second deflection coil system 13 this means that the field varies as a function of the location as shown in FIGS. Zu-c. FIG. 2a shows the field lines on the rear of the deflection system 7, that is to say in a cross-section at the area of the line (1-0 in FIG. 1. It is clearly shown that the shape of the field is cushionlike at this area. On the front of the deflection system. at the area of the line cc. however, the field has a barrel-like shape (see FIG. 20). whilst somewhere between these two extremes there is a section (h-b) where the field is homogeneous. For the sake of clarity, the diameters of the diagrams of FIGS. Za-c are shown to be equal, even though the corresponding sections are ob viously of different diameter.

The variation of the vertical deflection field shown in FIG. 2 appears in that the coils constituting the second deflection coil system are wound such that they can be comparatively readily manufactured and produce little raster distortion whilst use is also made, so as to satisfy also the convergence requirements, of a ring core 9 which is shaped as shown in a side elevation in FIG. 3 and in a rear view in H0. 4, and which determines the desired cushionlike distortion of the field on the rear of the deflection system. To this end. the ring core 9 is provided on its rear with two recesses which are situated such that their connecting line is situated in the horizontal plane. The shape and the dimensions of the recesses 15 determine the field in the rearmost part of the deflection system. It was found that. so as to avoid disturbing side-effects. the boundary of the recess 15 should preferably be a smooth line. The largest width of the recess 15, denoted by a in FIGS. 3 and 4. deter mines the degree of curvature of the lines of force in the diagram shown in FIG. 2av In a deflection system comprising saddle-like deflection coils, like in the embodiment shown, it was found that this dimension should be between one third and nine tenths of the outer diameter d of the rearmost part of the ring core 9. The depth 11 of the recess 15 is dependent of the size of the display screen of the tube. As the dimensions of this display screen are smaller, it appears that the value of 11 must be higher.

For a display tube having a display screen diagonal of 66 cm and a ring core with d=76 mm. the best results were obtained with the following dimensions of the recesses: a=50 mm (so approximately d) and 11 15 What is claimed is:

l. A device for the display of colour television images. comprising a cathode-ray tube of the shadow mask type having a rearmost cylindrical part in which a plurality of electron guns are arranged for generating a plurality of electron beams which are situated substantially in one plane. and a foremost flared part, the said device furthermore comprising a deflection system which is coaxially arranged about the tube near the transition between the two parts of the tube and which essentially comprises an annular ferromagnetic core having a cylindrical rear section. a first deflection coil system for deflecting the electron beams in a first deflection direction perpendicular to the tube axis and in the said plane, and a second deflection coil system for deflecting the electron beams in a second deflection direction perpendicular to the tube axis and to the said plane, the said deflection system being adapted such that the second deflection coil system generates a magnetic field which has a cushion-like shape near the rear of the deflection system and a barrel-like shape near the front. characterized in that the rear of the ring core has recesses in two diametrically situated locations, the connecting line between the recesses being substantially situated in the plane of the electron beams, said recesses having a depth at least equal to half the length of the rear section.

2. A device as claimed in claim 1. characterized in that the boundary of the recesses is a smooth line.

3. A device as claimed in claim 1, characterized in that each of the deflection coil systems comprises a pair of saddle-like, diametrically arranged deflection coils. the largest width of each of the recesses amounting to at least to one third of the outer diameter of the rearmost part of the ring core and at the most to nine tenths of said diameter.

4. A device as claimed in claim 3, characterized in that the said largest width is substantially equal to two thirds of the said diameter.

5. A deflection device for coaxial disposition about the transition between two parts of a cathode-ray tube having a rearmost cylindrical part in which a plurality of electron guns are arranged for generating a plurality of electron beams which are situated substantially in one plane. and a foremost flared part, said device comprising an annular ferromagnetic core having a cylindrical rear section, a first deflection coil system means disposed on said core for deflecting the electron beams in a first deflection direction perpendicular to the tube axis and in said plane, and a second deflection coil sys tem means disposed on said core for deflecting the electron beams in a second deflection direction perpendicular to the tube axis and to said plane and for generating a magnetic field which has a cushion-like shape near the rear of the deflection device and a barrel-like shape near the front. the rear of the ring core having recesses disposed in two diametrically situated locations, the recesses defining a plane substantially situated in the plane of the electron beams, said recesses having a depth at least equal to half the length of the rear section.

6. A device as claimed in claim 5, wherein each of the recesses comprises a smooth line boundary.

7. A device as claimed in claim 5 wherein each of the deflection coil systems comprises a pair of saddle-like diametrically arranged deflection coils, each of the recess having a largest width at least equal to one third of the outer diameter of the rearmost part of the ring core and at the most equal to nine tenths of said diameter.

8. A device as claimed in claim 7, wherein said largest width is substantially equal to two thirds of said diameter. 

1. A device for the display of colour television images, comprising a cathode-ray tube of the shadow mask type having a rearmost cylindrical part in which a plurality of electron guns are arranged for generating a plurality of electron beams which are situated substantially in one plane, and a foremost flared part, the said device furthermore comprising a deflection system which is coaxially arranged about the tube near the transition between the two parts of the tube and which essentially comprises an annular ferromagnetic core having a cylindrical rear section, a first deflection coil system for deflecting the electron beams in a first deflection direction perpendicular to the tube axis and in the said plane, and a second deflection coil system for deflecting the electron beams in a second deflection direction perpendicular to the tube axis and to the said plane, the said deflection system being adapted such that the second deflection coil system generates a magnetic field which has a cushion-like shape near the rear of the deflection system and a barrel-like shape near the front, characterized in that the rear of the ring core has recesses in two diametrically situated locations, the connecting line between the recesses being substantially situated in the plane of the electron beams, said recesses having a depth at least equal to half the length of the rear section.
 2. A device as claimed in claim 1, characterized in that the boundary of the recesses is a smooth line.
 3. A device as claimed in claim 1, characterized in that each of the deflection coil systems comprises a pair of saddle-like, diametrically arranged deflection coils, the largest width of each of the recesses amounting to at least to one third of the outer diameter of the rearmost part of the ring core and at the most to nine tenths of said diameter.
 4. A device as claimed in claim 3, characterized in that the said largest width is substantially equal to two thirds of the said diameter.
 5. A deflection device for coaxial disposition about the transition between two parts of a cathode-ray tube having a rearmost cylindrical part in which a plurality of electron guns are arranged for generating a plurality of electron beams which are situated substantially in one plane, and a foremost flared part, said device comprising an annular ferromagnetic core having a cylindrical rear section, a first deflection coil system means disposed on said core for deflecting the electron beams in a first deflection direction perpendicular to the tube axis and in said plane, and a second deflection coil system Means disposed on said core for deflecting the electron beams in a second deflection direction perpendicular to the tube axis and to said plane and for generating a magnetic field which has a cushion-like shape near the rear of the deflection device and a barrel-like shape near the front, the rear of the ring core having recesses disposed in two diametrically situated locations, the recesses defining a plane substantially situated in the plane of the electron beams, said recesses having a depth at least equal to half the length of the rear section.
 6. A device as claimed in claim 5, wherein each of the recesses comprises a smooth line boundary.
 7. A device as claimed in claim 5 wherein each of the deflection coil systems comprises a pair of saddle-like diametrically arranged deflection coils, each of the recess having a largest width at least equal to one third of the outer diameter of the rearmost part of the ring core and at the most equal to nine tenths of said diameter.
 8. A device as claimed in claim 7, wherein said largest width is substantially equal to two thirds of said diameter. 